The long-term objective of this laboratory is to elucidate the mechanism of signal transduction mediated by the proto-oncogene Wnt-1 (int-1). The Wnt-1 gene is of great interest because it is required for brain development and is one of the most frequently activated proto-oncogenes in Mouse Mammary Tumor Virus (MMTV) derived breast tumors. Wnt-1 is a member of a family of genes which display complex patterns of expression during embryogenesis and have been shown to be required for central nervous system, kidney and limb development. Several Wnt genes are expressed in the developing mammary gland. The Wnt-1 gene product is secreted and plays a role in cell-cell communication. This has also been shown for its Drosophila homolog wingless (wg), a segment polarity gene. Genetic studies in Drosophila have identified several segment polarity genes that are in the wg signal transduction pathway. These genes include dishevelled (dsh), zestewhite 3, armadillo, and engrailed, all of which have mammalian homologs. To date, dsh is the closest upstream component to the wg receptor. There are three mammalian dsh homologs (Dvl-1, Dvl-2, and Dvl-3), whose expression patterns are consistent with playing a role in Wnt-1 signal transduction. The goal of this proposal is to determine the function of the Dvl genes with respect to their roles in development, Wnt signal transduction and mammary tumorigenesis. The Specific Aims of this proposal are as follows: 1) identify and characterize proteins that interact with the Dvl gene product, using the yeast two-hybrid system to screen cDNA libraries; 2) analyze the function of Dvl by altering its expression levels in Wnt-responsive C57MG mammary epithelial and PC12 rat pheochromocytoma cell lines; 3) analyze the role of Dvl genes in development and Wnt signal transduction by generating knockout mice; 4) analyze the effect of Dvl null alleles on the onset and progression of mammary tumors in MMTV-Wnt transgenic mice. As the Wnt genes are involved in a number of developmental processes and mammary tumorigenesis, understanding its signalling pathway should lead to insights into these processes.